W126 shutdown gremlin?
 

1985 500SEL.

For whatever reason my W126 continues running with key removed and the ACC engaged/on. Push the button to turn off the ACC and it shuts down. I'm used to it so I don't care but it has resulted into some panicked calls from friends who have borrowed the car.

Any ideas? I'm sure it is back feeding somewhere through a relay but I'm stumped as to which one or ones.

It has a new ignition switch due to a different problem but it did it before and after the switch was replaced.

I assume that your car has an Over Voltage Protection relay. If it does, i would start by replacing it with a new one. If that does not fix the problem, try disconnecting the small wire that feeds the alternator light. The last time i faced this problem the diode bridge in the alternator had burned over and did not stop charging when the ignition switch was turned off, it was bleeding +12 volts through the small wire. If you need more info feel free to PM me.

Makes sense. I'll give those two items a try.

Oops! I did it to myself.:o A previous owner had hacked into the over heat/condenser fan wiring harness and I straightened out the mess (I thought). I think I used a regular ground instead of using the A/C pressure switch.

Found out by unplugging the relay I had re-wired. Back to the soldering iron!